Planar connectors, including flexible connectors, mechanical connectors and elastomer interposer connectors, are used in high density electric input/output applications where, because of space limitations, traditional connector technology is incapable of providing the required density. For example, in FIG. 1 a flexible interconnect 10 is part of a multi-chip unit (MCU) and provides connection between a high-density signal carrier (HDSC) 22 of the MCU and bumped gold contacts 32 on the interconnect 10. Interconnect 10 is comprised of flexible copper interconnect wires 12 integrated on an insulative polyimide film 14. The wires terminate at bumped gold contacts 32 which are distributed along a flat connection surface of the interconnect 10. The flexible interconnect 10 extends over a spring member, or more commonly, as shown in FIG. 1, an elastomer 16. The MCU is mated with a planar module 20 such that the gold bump contacts make conductive contact with gold-plated conductive pads on the side of the planar module 20 facing the interconnect 10. The elastomer 16 provides an opposing contact normal force for pressing the gold bumps on interconnect circuit 10 against the gold-plated pads 18 of the planar module 20.
A problem inherent in this technology is that the quality of the electrical contacts is often not uniform across the planar connection surface of the interconnect 10. This is particularly true when an elastomer 16 is used to support the interconnect. Such elastomers creep with age and applied pressure, and also can take on a set. That is, elastomers are not fully elastic and after compression, they do not return to their original shape. The amount of compression set is not constant and batch-to-batch variations can be significant. The resistance at each contact point on the interconnect is inversely proportional to the force normal to the planar connection. Hence, the resulting electrical integrity of the interconnect depends on the physical properties of the elastomer, and variations in this material will manifest equivalent variations in signal connection integrity.
In planar flexible connector technology, a method of gaining access to the mating interface without disturbing the interface for the purpose of measuring contact force does not appear to be commercially available. Consequently, a need exists for a method and apparatus for measuring the distribution of forces on contact surfaces or to measure changes in forces as functions of time, number of matings or torquing force.